Are you learning Koine Greek, the Greek of the New Testament and most other post-classical Greek texts? Whatever your level, use this forum to discuss all things Koine, Biblical or otherwise, including grammar, textbook talk, difficult passages, and more.

I reject the idea that there is a difference between learning Attic and Learning Koine. Nobody is going to learn to read Greek texts by working through one text book. Even if all you wanted to read is the Greek New Testament, you would still wind up looking at other texts like Athenaze and Chase and Phillips simply because they are good books which will improve your Greek. Anything in between Homer and say, 1086, to pick a date out of the air, can be read by anybody who is serious about reading Greek, and anybody who is serious about reading Greek will wind up being exposed to a variety of grammars and texts and vocab. Anybody who is serious about Greek will read Homer, for that matter, because once your Greek gets good enough the transition to Homer is not that hard.

So, all Greek is useful for all Greek. A little Greek won't be of much use in reading any Greek texts.

My stab at it:a) I don't know how good Mounce's basics is. As you can well understand yourself, since we're talking about "basics", you'll probably need at least one other textbook to get into more advanced stuff, even if Mounce's is the best around. But I'm sure I'm not telling you anything you don't know already so let's move to

b) Will knowing Koine help you with Greek of other periods? Depends on what you mean.

i. Homeric Greek (that is, if you are interested If not, it's not a crime/cardinal sin/whatever. De gustibus .... Not so much. Yes, it will help, in a structural level, but be prepared to be bewildered by the vocabulary at first. Apart from that, Homer tends to spell things out more, than, let's say John so, from a very specific and rather narrow point of view, it'll actually be easier than his gospel or some of the Epistles

ii. Attic/Ionic/Doric/Aeolic Greek (of which the most prominent is, of course, Attic). Will it help. Yes, most definitely so. Not without some extra reading for specific grammatical phenomena and types that where simplified by the time of Koine. I also don't know how interested you are in using the "correct" reconstructed pronunciation. If you are and you are not using the standard reconstructed one which is used (incorrectly) for any form of Greek that can be called ancient as opposed to the reconstructed Koine one, then, well, you'll have to learn the new one. Hardly anyone bothers though but I thought I'd mention it.

iii. Hellenistic. Almost the same as ii but not so much. Way closer to Koine, especially if we're near or at Roman times.

iv. Byzantine Greek. There are some writers who preferred to write in Attic Greek. Apart from those, with knowing Koine, you are golden. You may have to check some vocabulary, especially when it comes to the titles of officials and such but that's it. If you have a smattering of Latin that becomes a child's play.

v. Modern Greek (I know you didn't ask but I add it for completion's sake ) Yes it will. It's more simplified than Koine, but you'll have to learn a thing or two. Also, depending on the pronunciation scheme you went for, you may need to study some on that field too (very close to reconstructed Koine, a rather long way from Attic and such).

In a nutshell; Any introductory book means you'll have to study extra. Knowing Koine helps a lot with other forms of ancient Greek but it's not as if you can just pick Plato and read through. Anyway, that's how I see it.

I just posted a new topic with this same question, but perhaps it would be better to ask it here. If a person has learned Koine Greek, are there any good resources that can help to bridge the gap between Koine and Attic, or Koine and Homeric, etc?